<!DOCTYPE html>
<html>
<head>
<script>
// Preserve the initial document.prerendering value.
const initial_document_prerendering = document.prerendering;

// Records if 'onprerenderingchange' event is triggered at least once.
let onprerenderingchange_observed = false;
document.addEventListener('prerenderingchange', e => {
  onprerenderingchange_observed = true;
});
</script>
</head>
</html>
